| Year | Title | Role | Notes |
| 1949 | The Chevrolet Tele-Theatre | | Episode: "His Name Is Jason" |
| 1958 | Colgate Theatre | Felix | Episode: "McCreedy's Woman" |
| 1959–1965 | The Third Man | Bradford Webster | 72 episodes |
| 1959 | Zorro | Don Carlos | 3 episodes |
| 1961 | Outlaws | Sam Twyfford | Episode: "Outrage at Pawnee Band" |
| Twilight Zone | The Doctor, George Alfred | 2 episodes |
| 1963 | The Lloyd Bridges Show | Walter W. Pike | Episode: "The Tyrees of Capitol Hill" |
| 1963–1965 | The Bill Dana Show | Mr. Phillips, Mr. Harris, King Edward | 40 episodes |
| 1963 | Bonanza | Charles Dickens | Episode: "A Passion for Justice" |
| 1968 | Bewitched | Johann Sebastian Monroe | Episode: "Samantha on the Keyboard" |
| Sir Leslie | Episode: “Paul Revere Rides Again” |
| 1965–1968 | Lost in Space | Zachary Smith | 83 episodes |
| 1969 | Lancer | Padraic McGloin | Episode: "The Black McGloins" |
| 1970 | Land of the Giants | The Piper | Episode: "Pay the Piper" |
| 1970 | Get Smart | The Ambassador | Episode: "How Green Was My Valet" |
| 1973 | Sanford and Son | Emile Bodet | Episode: "Pot Luck" |
| 1975–1976 | Uncle Croc's Block | Basil Bitterbottom | |
| 1976 | Ark II | Fagon | Episode: "The Flies" |
| 1976 | Monster Squad | The Astrologer | Episode: "The Astrologer" |
| 1977 | Space Academy | Commander Isaac Gampu | 15 episodes |
| 1978–1979 | Battlestar Galactica | Lucifer (voice) | 9 episodes (uncredited) |
| 1984 | Diff'rent Strokes | Frankenstein's Creature (voice) | Episode: "Hooray for Hollywood" (uncredited) |
| 1985 | Challenge of the GoBots | Professor Janus (voice) | Episode: "Terror in Atlantis" |
| 1986 | Rainbow Brite | Count Blogg (voice) | 3 episodes |
| 1986–1987 | Foofur | Lance Lyons (voice) | 26 episodes |
| 1987 | Visionaries: Knights of the Magical Light | Mortdredd, Wizasquizar, Dark Bishop (voice) | 13 episodes |
| 1988 | BraveStarr | Professor Moriarty (voice) | Episode: "Sherlock Holmes in the 23rd Century" |
| 1989–1990 | Paddington Bear | Additional voices | 2 episodes |
| 1991 | Darkwing Duck | Phineas Sharp (voice) | Episode: "In Like Blunt" |
| 1996 | The Spooktacular New Adventures of Casper | Omar (voice) | Episode: "Poil Jammed/The Who That I Am/A Picture Says a Thousand Words" |
| 1996 | Mighty Ducks | Lord Gargan (voice) | Episode: "The Final Face Off" |
| 1996–1997 | Freakazoid! | Professor Jones (voice) | 6 episodes |
| 1996 | The Mask | The Devil (voice) | 2 episodes |
| 1996 | Quack Pack | Professor Henry Villanova (voice) | Episode: "Transmission Impossible" |
| 1997 | Superman: The Animated Series | Julian Frey (voice) | Episode: "Target" |
| 1997 | Extreme Ghostbusters | The Salesman (voice) | Episode: "Be Careful What You Wish For" |
| 1997 | Spider-Man: The Animated Series | Miles Warren (voice) | Episode: "The Return of Hydro-Man" |
| 1997 | Waynehead | Mr. Hollandopolis (voice) | Episode: "To Be Cool or Not to Be" |
| 1997 | Channel Umptee-3 | Stickley Rickets (voice) | 13 episodes |
| 1997 | The Angry Beavers | Julius Caesar (voice) | Episode: "Friends, Romans, Beavers!" |
| 1999 | The New Woody Woodpecker Show | Maxie the Polar Bear (voice) | Episode: "Chilly to Go" |
| 2000 | Buzz Lightyear of Star Command | Era (voice) | 2 episodes |
| 2006 | Danger Rangers | voice) | Episode: "Mission 547: Safety Rules"; posthumous release |
